4,279 research outputs found
A Blockchain-based Approach for Data Accountability and Provenance Tracking
The recent approval of the General Data Protection Regulation (GDPR) imposes
new data protection requirements on data controllers and processors with
respect to the processing of European Union (EU) residents' data. These
requirements consist of a single set of rules that have binding legal status
and should be enforced in all EU member states. In light of these requirements,
we propose in this paper the use of a blockchain-based approach to support data
accountability and provenance tracking. Our approach relies on the use of
publicly auditable contracts deployed in a blockchain that increase the
transparency with respect to the access and usage of data. We identify and
discuss three different models for our approach with different granularity and
scalability requirements where contracts can be used to encode data usage
policies and provenance tracking information in a privacy-friendly way. From
these three models we designed, implemented, and evaluated a model where
contracts are deployed by data subjects for each data controller, and a model
where subjects join contracts deployed by data controllers in case they accept
the data handling conditions. Our implementations show in practice the
feasibility and limitations of contracts for the purposes identified in this
paper
Negative thermal expansion in the Prussian Blue analog Zn3[Fe(CN)6]2: X-ray diffraction and neutron vibrational studies
The cubic Prussian Blue (PB) analog, Zn3 [Fe(CN)6]2, has been studied by
X-ray powder diffraction and inelastic neutron scattering (INS). X-ray data
collected at 300 and 84 K revealed negative thermal expansion (NTE) behaviour
for this material. The NTE coefficient was found to be -31.1 x 10-6 K-1. The
neutron vibrational spectrum for Zn3[Fe(CN)6]2.xH2O, was studied in detail. The
INS spectrum showed well-defined, well-separated bands corresponding to the
stretching of and deformation modes of the Fe and Zn octahedra, all below 800
cm-1.Comment: 4 pages, 3 figure
A Spectrophotometric Method to Determine the Inclination of Class I Objects
A new method which enables us to estimate the inclination of Class I young
stellar objects is proposed. Since Class I objects are not spherically
symmetric, it is likely that the observed feature is sensitive to the
inclination of the system. Thus, we construct a protostar model by carefully
treating two-dimensional (2D) radiative transfer and radiative equilibrium. We
show from the present 2D numerical simulations that the emergent luminosity
L_SED,which is the frequency integration of spectral energy distribution (SED),
depends strongly on the inclination of the system i, whereas the peak flux is
insensitive to i. Based on this result, we introduce a novel indicator f_L,
which is the ratio of L_SED to the peak flux, as a good measure for the
inclination. By using f_L, we can determine the inclination regardless of the
other physical parameters. The inclination would be determined by f_L within
the accuracy of +- 5 degree, if the opening angle of bipolar outflows is
specified by any other procedure. Since this spectrophotometric method is
easier than a geometrical method or a full SED fitting method, this method
could be a powerful tool to investigate the feature of protostars statistically
with observational data which will be provided by future missions, such as
SIRTF, ASTRO-F, and ALMA.Comment: 14 pages, 9 figures, accepted by Ap
Socially Optimal Mining Pools
Mining for Bitcoins is a high-risk high-reward activity. Miners, seeking to
reduce their variance and earn steadier rewards, collaborate in pooling
strategies where they jointly mine for Bitcoins. Whenever some pool participant
is successful, the earned rewards are appropriately split among all pool
participants. Currently a dozen of different pooling strategies (i.e., methods
for distributing the rewards) are in use for Bitcoin mining.
We here propose a formal model of utility and social welfare for Bitcoin
mining (and analogous mining systems) based on the theory of discounted
expected utility, and next study pooling strategies that maximize the social
welfare of miners. Our main result shows that one of the pooling strategies
actually employed in practice--the so-called geometric pay pool--achieves the
optimal steady-state utility for miners when its parameters are set
appropriately.
Our results apply not only to Bitcoin mining pools, but any other form of
pooled mining or crowdsourcing computations where the participants engage in
repeated random trials towards a common goal, and where "partial" solutions can
be efficiently verified
Modelagem computacional para simulação da produtividade potencial de cana-de-açucar.
Neste trabalho, um modelo ecofisiológico-matemático (BrCane) desenvolvido por Silva (2008) é utilizado para predizer a produtividade potencial - sem restrições nutricionais ou de água, a fim de analisar a sustentabilidade da expansão do cultivo de cana-de-açúcar em novas áreas para produção de etanol
Predição da produtividade da cana-de-açucar e da soja na reforma através da calibração e simulação do modelo CropSyst.
No presente trabalho, a biometria da cana-de-açúcar (Glycine max) é utilizada para a construção das curvas de biomassa, Ãndice de área foliar (IAF) e de produtividade no plantio de cana, utilizando-se a plataforma de simulação CropSyst
The superconducting phase of Calcium under the pressure at 200 GPa: the strong-coupling description
The thermodynamic parameters of the superconducting state in Calcium under
the pressure at 200 GPa have been determined. The numerical analysis by using
the Eliashberg equations in the mixed representation has been conducted. It has
been stated, that the critical temperature () decreases from 36.15 K to
20.79 K dependently on the assumed value of the Coulomb pseudopotential
(). Next, the order parameter near the temperature of zero
Kelvin () has been obtained. It has been proven, that the
dimensionless ratio decreases from 4.25 to 3.90
together with the growth of . Finally, the ratio of the electron
effective mass to the electron bare mass () has been
calculated. It has been shown, that takes the high value in
the whole range of the superconducting phase's existence, and its maximum is
equal to 2.23 for T=T_{C}.Comment: 5 pages, 5 figure
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